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authorLai Jiangshan <laijs@cn.fujitsu.com>2011-03-18 11:15:47 +0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-05-05 23:16:59 -0700
commit9ab1544eb4196ca8d05c433b2eb56f74496b1ee3 (patch)
treebe3a7897cf52920df4da41ded060e23150bdb849 /kernel
parent6cc68793e380bb51f447d8d02af873b7bc01f222 (diff)
downloadop-kernel-dev-9ab1544eb4196ca8d05c433b2eb56f74496b1ee3.zip
op-kernel-dev-9ab1544eb4196ca8d05c433b2eb56f74496b1ee3.tar.gz
rcu: introduce kfree_rcu()
Many rcu callbacks functions just call kfree() on the base structure. These functions are trivial, but their size adds up, and furthermore when they are used in a kernel module, that module must invoke the high-latency rcu_barrier() function at module-unload time. The kfree_rcu() function introduced by this commit addresses this issue. Rather than encoding a function address in the embedded rcu_head structure, kfree_rcu() instead encodes the offset of the rcu_head structure within the base structure. Because the functions are not allowed in the low-order 4096 bytes of kernel virtual memory, offsets up to 4095 bytes can be accommodated. If the offset is larger than 4095 bytes, a compile-time error will be generated in __kfree_rcu(). If this error is triggered, you can either fall back to use of call_rcu() or rearrange the structure to position the rcu_head structure into the first 4096 bytes. Note that the allowable offset might decrease in the future, for example, to allow something like kmem_cache_free_rcu(). The new kfree_rcu() function can replace code as follows: call_rcu(&p->rcu, simple_kfree_callback); where "simple_kfree_callback()" might be defined as follows: void simple_kfree_callback(struct rcu_head *p) { struct foo *q = container_of(p, struct foo, rcu); kfree(q); } with the following: kfree_rcu(&p->rcu, rcu); Note that the "rcu" is the name of a field in the structure being freed. The reason for using this rather than passing in a pointer to the base structure is that the above approach allows better type checking. This commit is based on earlier work by Lai Jiangshan and Manfred Spraul: Lai's V1 patch: http://lkml.org/lkml/2008/9/18/1 Manfred's patch: http://lkml.org/lkml/2009/1/2/115 Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: David Howells <dhowells@redhat.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcutiny.c2
-rw-r--r--kernel/rcutree.c2
2 files changed, 2 insertions, 2 deletions
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 0c343b9..4d60fbc 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -167,7 +167,7 @@ static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)
prefetch(next);
debug_rcu_head_unqueue(list);
local_bh_disable();
- list->func(list);
+ __rcu_reclaim(list);
local_bh_enable();
list = next;
RCU_TRACE(cb_count++);
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index b579e4f..2c07adb 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1206,7 +1206,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
next = list->next;
prefetch(next);
debug_rcu_head_unqueue(list);
- list->func(list);
+ __rcu_reclaim(list);
list = next;
if (++count >= rdp->blimit)
break;
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